Control apparatus for electrostatic drying



Aug. 5, 1941. G. "r. HART, JR., ETAL 2,251,277

CONTROL APPARATUS FOR ELECTROSTATIC DRYING Filed Jan. 24, 1939 FRE QUENCY OSCILLATOR Patented Aug. 5, 1941 CONTROL APPARATUS FOR ELECTRO-STATIC DRYING George T.

Lynn, Masa, ery Corporation,

Hart, Jr., and Erastus E. Winkley,

assignors to United Shoe Machln- Borough of Flemington, -N. 1.,

a corporation of New Jersey Application January 24, 1939, Serial No.252,605

Claims.

This invention relates to the control of an apparatus arranged toproduce an electrostatic field for drying or otherwise treating a seriesof articles, in order that the output of the apparatus which producesthe field may be varied in response to changes in the demands of theload.

The use of a high frequency electrostatic field for the purpose ofdrying articles is well understood and when such an apparatus isemployed commercially it follows that it will be utilized commonly for alarge number of articles which frequently are not presentedsimultaneously to the fleld but are added one after another. Such anapparatus is employed for drying shoes, for example, and then the loadwill vary as successive shoes are presented to the field and theresultant changes in the load will depend not only upon the number ofarticles presented but also on the quantity of moisture in the variousarticles, which, in the case of shoes being bottomed, is locatedprincipally in their outsoles. The quantity of moisture in turn willdepend partly upon the sizes of the shoes being treated and partly uponthe quality of the material, because of the diiierent absorptive powersof different types of leather, as well as upon the way the shoes are puttogether and other factors. The demand for power created by thesevarious factors will for convenience be termed the shoeor work-load. Inconsidering the problem, it will be convenient to think of the variousarticles as included in a single electrostatic field, that is to say, afield produced merely by one pair of electrodes. The problem is,however, not substantially diiferent where pairs of electrodes areprovided for single articles and a plurality of these electrodes arejoined in parallel and connected to a single source of supply, such as ahigh frequency oscillator.

In one physical embodiment of an apparatus for. this purpose, cars of aconveyor are provided for supporting pairs of shoes and each car haselectrodes associated with the respective shoes, these electrodes beingjoined to a single oscillator by means of a trolley and live railarrangement. There will further be no substantial diiTerence in theproblem of control of output if the shoe supports are mounted in fixedpositions, or, if electrodes are provided for association with shoespositioned upon the ordinary shoe racks so commonly used in shoefactories.

It will be understood that, in designing a conveyor for drying articles,the number of cars pmvided is more than sufificient to take care of theregular run of work during an interval such as ..the' various articlesis to be kept substantially constant so that they may be removed fromthe cars returning along the lower run of the conveyor as these carsreach the loading station. As moist articles are presented to thesystem, the

load increases; as theydry out, the load is correspondingly reduced. Atany particular settin of the oscillator, an electrostatic field ofcertain intensity is produced and if this field is shared by a pluralityof wet articles, the active power in each article will be less thanwould be the case if a lesser number of articles were within the fieldand the oscillator must be adjusted to meet the needs of the greaterload.

One important object of the invention is to provide a controlorganization for use with a high frequency source whereby the action ofthe field on the articles, such as shoes, is substantially unaflected byvariations in the load as determined by the various factors mentionedabove.

To this end, and in accordance with a feature of the invention,automatic means is provided which is responsive to changes in thedemands of the load and is arranged to vary the output of the oscillatorto meet its demands.

Other features of the invention reside in employment of apparatus whichis responsive to changes of the output current of the oscillator whichsupplies the electrodes, these changes operating to regulate the voltageapplied so that the efliciency of the field will be maintained and thedrying time will be substantially uniform.

Still another object of the invention is to devise an improved method ofdrying articles by means of an electrostatic field in accordance withwhich the drying time for the various articles is rendered substantiallyconstant by automatically varying the effectiveness of the field as theload changes.

In another aspect, the novel method consists in applying the field to achanging number oi! articles and in automatically maintaining theeffectiveness of the field as the load imposed by the articles changes.

The way in which this method may be carried out'and an illustrativeapparatus which may be employed, will now be described in the i'ollowingspecifiecation taken in connection with the drawing.

lnthesinglefla'iireoithisdrawingtypical control apparatus has been showna cally There, a high frequency oscillator I90 of any well-knownconstruction receives power from wires I52 leading from a source ofalternatingcurrent power of ordinary commercial frequency and delivershigh frequency current to live rails 60 and H4 typiiying the electrodesin association with which the articles are positioned for treatment. Itwill be assumed, tor the sake of illustration, that the oscillator I isof the sellexcited type and involves vacuum tubes of wellknownconstruction, the filaments of which are supplied with power throughleads I64.

In our arrangement for automatically controlling the output of theoscillator in accordance with the shoe or work-load present between theelectrodes, an ammeter IE6 is inserted in the circuit between theoscillator and one of the live rails and, hence, is responsive to thevarying load. This ammeter I60, indicating changes in output current, isprovided with a mirror I60 mounted to be tilted as the needle oi theammeter moves, thereby to vary the angle of reflection of a beam oflight received from a lamp I10 focused by a lens system "2 on a smallarea of the mirror and reflected therefrom through a V-slot I14 in aplate I10 for reception by the cathode I18 of a photoelectric tube I00having the usual anode I19. It will be seen that the slot I14 is widerat the top than at the bottom and as the current in the ammeterdecreases, the mirror will be tilted counterclockwise to pass the beamof light through the upper part of the slot thereby throwing more lighton the cathode and causing a greater current to flow through the tubeI80. Current passing through the photoelectric tube I00 is amplified bya thermionic tube I02 in the usual manner. The plate currents for thephotoelectric tube I00 and the amplifier tube I02 are supplied from thetransformer secondary winding I84, one end of which is connected to thedirect current winding I90 oi the saturable reactance I92 and thence tothe anodes of the tubes I00 and I82, the other end being connected tothe mid point of the filament transformer I94 and to one end of thepotentiometer I96. The other end of the potentiometer is connected backto a tap in the transformer winding I94. Adjustment of the potentiometerdetermines the voltage impressed on the anode of the photoelectric tubeI80. Because of the rectiiying action of the tubes, it is obvious thatpulsating direct current flows in the winding I90 0! the saturablereactance I92.

The alternating current coil 200 of the saturable reactance is suppliedwith power from another transiormer secondary 202. A condenser 204 and anon-inductive resistance 200 are in series with the reactance coil 200and the primary of a grid transformer 2I0 is connected between a midpoint of the secondary coll 202 and a point between the condenser 204and the resistance 206 in the circuit of the coil 200 of the saturablereactance. It will be understood that the saturable reactance I92, in awell understood fashion, responds to small changes in the currentflowing through the direct current coil I90, thereby producing largechanges in the current delivered to the grid transformer 2I0. Thesecondary oi the grid transformer 2I0 is connected to the grids of apair of thyratron tubes 2I2, the filaments of which are supplied from atransformer secondary 2. These tubes act to supplymore orless currentfrom a transformer secondary 220 to the input circuit 222 of theoscillator I00. To this end, the terminals of the secondary 220 areconnected to the plates of the thyrat-ron tubes 2I2 and the inputcircuit 222 derives its power in a well-understood fashion by reason ofconnections to a mid point 224 in the secondary 220 and a point 228 in alead connecting the filaments of the thyratron tubes. A switch I40 is inseries with this input circuit of the oscillator.

It will be understood, however, that the particular control circuitsherein shown by way of illustration are not the only ones which may beused and that other well-known arrangements may be substituted forenabling variations in load to control the output of the oscillator. Forexample, in oscillators where the load imposed requires a smalleroutput, the thyratron tubes together with their transformers could bedispensed with and the alternating current windings 200 01 the saturablereactance I92 be connected directly to the input terminals 222 of theoscillator I60 by connecting together the points a, a and alsoconnectlng the points I), b, thus accomplishing the same result in thesmaller power range, Any preferred arrangement which provides forautomatically increasing the output power of the oscillator as the workload increases and corresponding- 1y decreasing the output power as thework load decreases, comes within the scope of this invention.

It is found that, where the greater part of the electrical capacity inthe output circuit of the oscillator is formed by the electricalcapacities of the articles, then the frequency of the current deliveredby the oscillator will be continually upset because of the change in theelectrical capacities of the articles as they dry. It has been founddesirable, therefore, especially in the case of a self -excitedoscillator, to provide a stabilizing condenser 230 bridged across theoutput side of the oscillator which will have a suillcient capacity sothat the capacity provided by the articles, such as shoes, is a smallpart of the total of the electrical capacity of the output circuit ofthe oscillator, As a consequence, changes in the capacities provided bythe articles as they dry will not unbalance the oscillator and cause itto operate inefliciently. The stabilizing condenser 230 is shov-ndiagrammatically as comprising a pair of plates, one of which may bemoved with respect to the other by rotating it about a supporting pin232. This adjustment is required chiefly during the setting up of theapparatus.

The action of the control apparatus will now be explained. As articles,such as shoes, are inserted between the electrodes, the effect on anoscillator circuit having a fixed input power is to increase the outputvoltage drop and consequently to reduce the output amperage. This wouldlengthen the drying time since there would be less power per article. Inthe illustrated method of regulating the output power so that drying isaccomplished in a uniform time regardless of changes in the work load,it is elected to adjust the power supplied to the input circuit of theoscillator. The ammeter I60, responding to changes of current in theoutput circuit, reflects more light to the photoelectric tube I as thework-load increases by adding wet articles, thus temporarily causing adecreased output current or less light as the load decreases during theprogress of the dryingout process. The electrical response of thephotoelectric tube Hill to the changing values of impinging light,amplified by the tube I82, will cause a controlled, pulsating, directcurrent to flow in the coil I90 the saturable reactance.

In this reactance I92, the construction is such that with no directcurrent fiowing in coils I50, the large amount of iron in the coreoffers a high impedance to the alternating current in coils 200 and sobut little current can fiow. As direct current is admitted to cells I90,a flux will be created that tends to saturate the iron, decreasing theimpedance of the alternating current coils 2M and, since the impedancedrop is inversely proportional to the total saturation of the iron, morealternating current will flow. As the direct current required is only afraction of one per cent of the alternating current controlled, thenecessary amount is readily supplied by the small currents in thephotoelectric tube I80 stepped up by the amplifier tube I82. Utilizing awell-understood principle of phase shifting, changes in the amount ofcurrent in the circuit which includes the inductance 200, thecapacitance 204, the resistance 2%, the primary of the grid transformer2H! and the transformer secondary 202, are effective to change the phaseof the grid currents with respect to the plate. currents in thethyratron tubes 212. As the phase of the grid current in the thyratronsaids or opposes the electron emission in those tubes, they will act as arheostat and more or less power will be supplied to the input circult222 of the oscillator Hill. This will result in energy at higherterminal voltages being impressed on the live rails 68 and H4 as wetarticles are added to the field and in a reduction of that voltage asthe drying process proceeds toward completion. Inasmuch as the change inthe alternating current flowing through the coil 200 of the saturablereactance is not a straightline change, the sides of the slot I14 in theplate "6 are not straight but have been curved arbitrarily to compensatefor the characteristics oi the saturable reactance I92.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent of the United States is:

1. In an apparatus for treating articles, electrodes between which sucharticles may be positioned, an oscillator for supplying high frequencycurrent to said electrodes to produce an electrostatic field passingthrough the articles, and automatic means responsive to changes in thedemands of the load and arranged to vary the output of the oscillator tomeet those de mands.

2. In an apparatus for treating articles, elec- 6 trodes in associationwith which articles may be positioned, an oscillator for supplying highfrequency current to said electrodes to produce an electrostatic fieldpassing through the articles, means for indicating changes in the outputof the oscillator, means for supplying current to the oscillator, andmeans, including a photoelectric cell, responsive to changes in saidinditating device and arranged to contfol the input to the oscillator.

3-. In an apparatus for treating articles electrically, means forproducing an electrostatic field within which a plurality of articlg maybe positioned, and a device, responsive to a current which isproportional to the output of said fieldproducing means, for regulatingthe amount of power delivered by said field-producing means.

4. In an apparatus for treating articles, electrodes in association withwhich articles may be positioned, means including an oscillator for delivering high frequency current to said electrodes, a device responsiveto changes in the output current of the oscillator as the load changes,means for delivering power to the oscillator, and means controlled bysaid device for varying the amount of power delivered to said electrodesas the output current is varied, thereby to keep the efi'ectiveness ofthe electrostatic field substantially constant.

5. That method of drying articles by means of an electrostatic fieldwhich consists in treating a plurality of articles in such a held, andin rendering the drying time for the various articles substantiallyconstant by automatically increasing the effectiveness of, the field asthe load increases.

6. That method of drying articles by mean of an electrostatic fieldwhich consists in treating a plurality of articles in such a field,indicating changes in a current flow as the article load changes, andautomatically adjusting the power supplied to the electrostatic field tomaintain that current substantially constant.

'7. That method of drying articles by means of an electrostatic field,which consists in applying the field to a changing number of articlesand automatically maintaining the efiectiveness of the field as the loadimposed by the articles changes.

8. That method of drying articles by means of an electrostatic field,which consists in treating a plurality of articles in such a field andin automatically adjusting the field in response to the changing loadprovided by the articles to dry the various articles in a substantiallyuniterm time.

9. That method of drying articles by means of an electrostatic field,which consists in applying the field successively to a plurality ofarticles which are wet and removing some of the articles which havebecome dry, and automatically adjusting the field in response to thechanging load provided by the articles to keep the efliciency of thefield substantially constant independent of the number of articles undertreatment.

10'. That method of drying articles by means of an electrostatic field,the power for which 0 is supplied by an oscillator, which consists inprogressively applying the field to additional articles which are wet,removing articles which have become dry, and automatically varying theoutput 0! the oscillator in response to the changing load provided bythe articles.

GEORGE T. HART. JR. ERASTUS E. WINKLEY.

. CERTIFICATE OF comcuori. Patent No. 2,251,277. August 5, 19141.

- GEORGE '1'. HART, .m., ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page},second column, lines Shand 55, claim 9, strike out the words "inresponse to the changing load providedby the articles"; and that thesaid Letters Patout should be read with this correction therein that thesame may conform to the record ofthe cesin the Patent Office.

Signed and sealed this mm day October, A. D. 19t

Henry Van Arsdale;

(Seal) Acting Commissioner of Patents

